Hydrocarbon such as methane, natural gas, petroleum gas, naphtha, heavy oil, crude oil or the like is reacted with a reforming agent such as water, air, carbon dioxide or the like at a high temperature zone in the presence of a catalyst, thereby reformed to a highly reactive mixture gas of carbon monoxide and hydrogen. The reformed mixture gas of carbon monoxide and hydrogen is used as a raw material of methanol, liquid fuel oil, etc. Recently, research and development to separate hydrogen gas for fuel cells from the mixture gas have been also performed. Reforming catalysts such as nickel/alumina, nickel/magnesia/alumina and the like have been used in a reaction of synthesizing the mixture gas of carbon monoxide and hydrogen.
In a hydrocarbon/steam reacting system using a reforming catalyst, a reaction by-product, i.e. carbonaceous matters, is likely to be deposited on a surface of a catalyst. The deposited carbonaceous matters cover active sites of the catalyst surface so as to reduce catalytic activity. Heavy deposition of the carbonaceous matters causes the clogging, damage and the like of a catalyst and also deviation of gases flowing in a reaction zone, which results in decreasing a proportion of the catalyst effective for reforming reactions. Deposition of the carbonaceous matters on the surface of the catalyst can be avoided by introducing an excess amount of steam, but introduction of excess steam unavoidably requires increases in an energy cost and needs larger facilities.
A reforming catalyst where a catalytically active component is highly dispersed has been proposed in order to inhibit deposition of carbonaceous matters without the introduction of excess steam (Patent Document 1 & 2). Patent Document 1 describes a method below to obtain a reforming catalyst wherein a catalytically active component is highly dispersed. A method is employed in which the catalyst is manufactured by adding a co-precipitating agent to an aqueous solution containing water-soluble salts with respect to each of elements constituting the catalyst particles so as to precipitate hydroxides and the first calcination of the precipitates in a temperature range of 673K to 873K and the second calcination of the precipitates in a temperature range of 1223K to 1573K. In the reforming catalyst described in Patent Document 2, a porous molded material (a catalyst carrier) is impregnated with an aqueous solution containing catalytically active components such as Ni, Co and the like and carrier-constituting components such as Mg, Al, Zr, Ti, Ca and the like to infiltrate the catalytically active component and the carrier-constituting components into the porous molded material. Then, the porous molded material is dried, calcined at a high temperature of at least 700° C. and then activated at 500° C. or higher, thereby to disperse fine particulate catalyst particles on a surface layer of the porous molded material. It is disclosed that the high dispersion of the catalyst particles inhibits the deposition of carbonaceous matters onto the catalyst surface and thus excellent catalytic activities are maintained over a long period.
PATENT DOCUMENT 1: Japanese Unexamined Patent Application, First Publication No. 2002-126528.
PATENT DOCUMENT 2: Japanese Unexamined Patent Application, First Publication No. 2004-141860.